1. Field of the Invention
The present invention relates to a wireless power feeder/receiver and a wireless power transmission system for performing power transmission by a non-contact method.
2. Related Background Art
Recently, transition to an electric vehicle is promoted for solving environmental problems (e.g., reduction of CO2 emission amount). For expanding use of the electric vehicle, it is desired to realize a secondary battery charging method which is simple and safe and also does not put a burden on a person (e.g., reduction of a burden to connect a relatively heavy charging cable or improvement of safety such as avoidance of electrification and the like). Accordingly, non-contact power feeding utilizing electromagnetic induction or a magnetic field resonance effect which is a kind of magnetic coupling (electromagnetic coupling), is drawing attention.
Further, a house employing a technique of storing natural energy such as solar power into a secondary battery and utilizing the stored energy for solving the environmental problems, is becoming popular. In this case, a secondary battery which has a large storage capacity for sufficiently storing natural energy is required and it is expected to use a secondary battery mounted on an electric vehicle. Also in this case, non-contact power feeding utilizing the electromagnetic induction or the magnetic field resonance effect which is a kind of magnetic coupling (electromagnetic coupling), is drawing attention.
In these cases of non-contact power feeding, it is desired to realize a wireless power feeder/receiver which is capable of easily selecting power feeding from a house as a base station to an electric vehicle or power feeding from the electric vehicle to the base station, that is, capable of easily performing bidirectional power transmission.
Meanwhile, in a wireless power transmission system utilizing the electromagnetic induction, a wireless power feeder is provided with a power feed coil and a wireless power receiver is also provided with a power receive coil, and then power transmission is performed by a non-contact (wireless) method by utilizing the electromagnetic induction between these power feed coil and power receive coil.
Further, in a wireless power transmission system utilizing the magnetic field resonance effect, a wireless power feeder is provided with a power feed resonance circuit having a power feed coil and a power feed capacitor and a wireless power receiver is also provided with a power receive resonance circuit having a power receive coil and a power receive capacitor, and then power transmission is performed by a non-contact (wireless) method utilizing the magnetic field resonance effect between these power feed resonance circuit and power receive resonance circuit. Note that, in this wireless power transmission system, the wireless power feeder may include an excitation coil for supplying power to the power feed resonance circuit and the wireless power receiver also may include a load coil receiving power from the power receive resonance circuit.
A wireless power transmission system utilizing this kind of magnetic field resonance effect is disclosed in International Patent Publication WO/2007/008646.
Further, each of Japanese Patent Application Laid-Open Publication No. 2011-19291 and Japanese Patent Application Laid-Open Publication No. 2010-183813 also discloses a wireless power transmission system utilizing this kind of magnetic field resonance effect.
In the wireless power transmission system disclosed in Japanese Patent Application Laid-Open Publication No. 2011-19291, each of plural wireless power receivers has a switch controlling feeding/non-feeding of AC power from a resonance circuit to a rectification circuit, and power receive timing is controlled for each of the wireless power receivers and power receive priority is changed for each of the wireless power receivers.
Further, the wireless power transmission system disclosed in Japanese Patent Application Laid-Open Publication No. 2010-183813 is a system for feeding power from a base station to an electric vehicle and estimates a positional relationship between the base station and the electric vehicle for efficiently charging a secondary battery mounted on the electric vehicle. Specifically, before performing power feeding from the base station to the electric vehicle, power transmission is performed sequentially to the base station by switching two sets of power receive coil mounted on the electric vehicle from an AC power source for distance measurement mounted on the electric vehicle, distances between a resonance coil on the base station side and the respective resonance coils on the electric vehicle side are estimated, and a positional relationship between the base station and the electric vehicle is estimated from these two estimated distances.